@media screen and (max-width: 1920px) {
  header {
    width: 100%;
    height: 300px;
    background-image: url("../images/big/logo.jpg");
    background-size: 100% 100%;
    -moz-background-size: 100% 100%;
    -webkit-background-size: 100% 100%;
  }
}
@media screen and (max-width: 960px) {
  header {
    width: 100%;
    height: 150px;
    background-image: url("../images/small/logo.jpg");
    background-size: 100% 100%;
    -moz-background-size: 100% 100%;
    -webkit-background-size: 100% 100%;
  }
}


